This invention relates to determining, by nondestructive test methods, the purity of composition of bars of material of a given shape; and more particularly, to determining whether a bar of precious metal has a purity of composition which is within a given range of variance from that of a standard bar of known purity of composition.
U.S. Pat. No. 3,981,175, issued Sept. 21, 1976 (hereby expressly incorporated by reference), discloses an apparatus for making such a nondestructive determination, wherein a standard bar, of known purity of composition, and a sample bar, whose purity of composition is desired, are both placed in a thermal chamber. A heat pulse of finite duration is applied to one end of both bars and the temperature vs. time responses of the opposite ends of both bars are monitored to determine the similarity of response. The patent recognizes, also, the possibility of sequential testing, in which the time vs. temperature response of a sample bar is compared with the previously stored time vs. temperature response of a standard bar.
The principal objects of the present invention are to provide an improved system for making such a comparison between the temperature response of a sample bar and the temperature response of a stored standard, and improved systems which may not use such a stored standard, wherein the measurements of temperature responses are improved by better control of heat losses, uniformity of temperature ranges, establishment of conditions of heat equilibrium, and better methods of temperature detection by the elimination of contact resistances.
Other objects of the present invention are improved systems for detecting tungsten forgeries and for determining the density, thermal conductivity, and heat capacity of a given material.